The third rail collection assembly is mounted on a railed vehicle for use as an electric current collector for running engagement with a third rail or electrical distribution rail. The third rail collection assembly includes a collection shoe or boot which is resiliently or retractably mounted to a support. The support includes a beam which acts as an insulator to prevent passive electrical contact between the third rail and the body of the railed vehicle. The passive electrical contact results in undesirable grounding between the third rail and the railed vehicle.
Heretofore, beams for use on the third rail assembly have traditionally been made of wood and more particularly oak. Oak has been used in the past for the beam because it is extremely strong and very rigid. Wooden beams, however, have many drawbacks for preventing electrical contact. One difficulty with the wooden beam is that as it is exposed to the elements and weathers, cracks are formed in the beam. Water, grease and other materials settle in the cracks and increase the conductivity of the beam thus promoting electrical arcing between the third rail and the railed vehicle. When the water in the cracks turns to ice it expands and increases the crack formation, thus increasing the surface area over which water or other conductive materials may be present in the beam.
Another difficulty occurs when the third rail collector shoe encounters an obstacle such as a rock, ice, or the like. When this occurs, the third rail collector shoe breaks off so that the railed vehicle will not be damaged. However, in addition to the third rail collector shoe breaking, the wooden beam arc shield tends to break or crack and thus needs to be replaced along with the collector shoe. Assembly and replacement of the wooden beam is difficult because the wooden beams are very heavy to lift resulting in excessive back strain or the need for heavy equipment.
U.S. Pat. Nos. 1,308,543 and 1,766,639 to Howe; and 4,546,706 to Jackson et al. disclose third rail assemblies having wooden beams. The wooden beams are mounted between the third rail collector assemblies and the body of the railed vehicle to prevent passive electrical contact.
Other patents which disclose further features and embodiments of various third rail collectors for use with railed vehicles include: U.S. Pat. Nos. 3,509,292 to Dehn; 3,089,005 to Dean et al.; 3,733,446 to Colovas et al.; 3,804,996 to Monteith; 4,526,108 to Spencer et al.; and 4,851,617 to Schmitt et al.
The above related art summaries are merely representative of portions of the inventions disclosed in each reference. In no instance should these summaries substitute for a thorough reading of each individual reference.